The overall goal of this surgery is to chronically instrument animals to allow for hemodynamic measurements during cardiopulmonary stress testing in alert animals with and without cardiovascular disease. This method can help answer key questions in the cardiovascular field, such as how metabolic syndrome affects left ventricular function and perfusion therby contributing to the development of heart failure with preserved ejection fraction. Two key advantages of this technique are that hemodynamic measurements and blood samples are obtained from awake animals and the technique can be performed at rest and during cardiovascular stress such as exercise.
The implications of this technique can extend towards early diagnosis of pulmonary hypertension because pulmonary microvascular function, as well as right ventricular function and perfusion can be measured at well defined stages after introduction of the disease. Visual demonstration of this technique is essential. It is difficult to learn how to place a flow probe around a coronary artery due to vasospasm of this vessel.
Also, placing the flow probe around aorta is difficult due to location of this vessel with respect to the thoracotomy. Demonstrating the procedure will be Annemarie Verzijl, a technician from our laboratory. After preparing the animal for surgery, make an incision in the skin, starting one centimeter caudal to the left inferior angle of the scapula and cut downward to the left axilla.
Following the incision, use diathermy to cauterize blood vessels in the skin. Next, using the cutting modality of the diathermy, cut though the serratus muscle and pectoralis major muscle. Continue using diathermy to cauterize blood vessels in the muscle layer.
Now, using blunt dissection, carefully divide the intercostal muscle of the 4th left intercostal space. Finish this using a mosquito clamp. Then expose the costal surface of the left lung, which is covered with visceral and parietal pleura.
Next, enter the pleural cavity by carefully piercing both layers of the pleura and tearing them open. Improve the exposure with a thoracic retractor by separting the edges of the wound and ribs then forcefully pushing the tissues apart. To expose the heart and great vessels, push the left lung caudally and wedge it in place with wet gauze.
Begin this portion of the surgery with a blunt dissection to remove about 2 square centimeters of connective tissue surrounding the descending thoracic aorta. Next, place a three stitch purse string suture in the aortic wall using non-absorbable USP 3-0 braided silk suture. Then penetrate the aortic vessel wall through the suture with a stainless steel, 16-gauge needle.
Following the needle, insert the tip of the fluid-filled catheter into the aorta. Then pull the purse string suture firmly together and tie it off. To secure the catheter, wind the excess suture around the catheter above the ring three times, tie it off, and add a new stitch about 1 centimeter cranial to its insertion site.
Now connect the fluid-filled catheter to the calibrated pressure transducer connected to a computer. Thus, monitor the mean arterial pressure during the subsequent steps. Next, without damaging the phrenic nerve, open the pericardium with a crossed cut.
Beneath the cut, expose the ascending aorta and aortic arch with a Farabeuf retractor by identifying the pulmonary artery and gently pulling it caudally. With the aorta exposed, make a 1 centimeter cut in the connective tissue between the ascending aorta and the pulmonary artery using Metzenbaum scissors. Now attach the flow probe.
first get the rubber band around the vessel by using a suture lead. And secondly, attach the flow probe measurement device to the rubber band. Thirdly, connect the flow probe to the computer and fourthly, check the cardiac output signal to confirm the probe is properly positioned.
The next step is to expose and dissect the proximal part of the left anterior descending coronary artery. First, lift the tissue with forceps. And then, using Metzenbaum scissors, make a small cut in the tissue.
Then carefully tease away tissues from the artery using a cotton swab. And to ensure the coronary artery is completely dissected, pass a small, straight-angled mosquito clamp underneath it. When vasospasm of the coronary artery occurs, spray with 10%lidocane to relax the vessel.
Using the same technique, place fluid-filled catheters in the pulmonary artery, right ventricle, left ventricle, and left atrium. All the catheters should now be connected to the computer. Then make a stitch parallel to the anterior interventricular coronary vein with a suture connected to the coronary venous catheter.
Following the stitch, puncture the vein with the 20-gauge needle of the coronary venous catheter and insert the cannula of the catheter intravenously. Then secure the catheter with the existing stitch. Remove the needle and connect to the extension line.
Now place a coronary flow probe around the previously dissected left anterior descending coronary artery. With the probe placed, check the signal of the coronary flow on the computer to confirm that the flow probe is correctly placed. The shape of the coronary flow signal should be similar to that shown here.
Begin this phase of the surgery by making a 1.5 centimeter incision about 8 centimeters caudal and parallel to the first incision. Then using a large, curved mosquito clamp, subcutaneously lead the drain from the pleural cavity through the 6th intercostal space to this incision. Connect the drain to the suction device to remove remaining fluid from the thorax.
Next, use a large, curved mosquito clamp to tunnel the flow probes individually through the 3rd left intercostal space and the muscle above the rib. Tunnel the fluid-filled catheters through either the 3rd or the 5th left intercostal space. Firstly, clamp off the fluid-filled catheters.
Next, remove the three-way stopcock to minimize the piercing area. And thirdly, pierce the intercostal muscle. Now, fix the flow probes and the fluid-filled catheters with non-absorbable USP 2-0 braided silk.
Use a purse string suture on the intercostal muscle. This sutre will also prevent air leakage after reinstating negative intrathoracic pressure. Next, make three incisions in the skin about 2 centimeters to the left and parallel to the vertebral column.
Make these three incisions 3 centimeters long and 3 centimeters apart from each other. Now pierce a trocar beneath the left latissimus dorsi muscle from the rostral incision site to the incisions on the back. Then using the trocar, tunnel the flow probes and fluid catheters to the back.
Once tunneling is complete, place stopcocks on the fluid-filled catheters and remove the clamp. Withdraw some blood to remove the clots and air bubbles. Then fill the fluid-filled catheters with heparin at 1, 000 units per milliliter, and fill the coronary venous catheters with heparin at 5, 000 units per milliliter.
Close the thorax by pulling together the ribs of the 4th intercostal space at two separate sites. Use non-absorbable USP 6 braided polyester. Then close the serratus muscle and pectoralis major muscle with the running stitch.
Close the skin with the running subcuticular suture using non-absorbable USP 2-0 braided silk. Then sutre the incisions on the dorsal side between the catheters. First, tie a knot directly onto the skin to close the incision.
Then fixate the catheters to the suture with another knot about 1 centimeter from the skin. Suture the flow probes with polyglactin suture so that the flow probe wire is not cut by the suture. Then carefully remove the drain while applying pressure to the cranial side of the incsion so as to reinstate negative pressure in the pleural cavity.
Now complete the surgery by closing the incision with a purse string suture and sealing the wound with petroleum jelly. Follow the text protocol on how to recover the animal and how to conduct the treadmill experiment. Exercising swine to move up to 5 kilometers per hour resulted in a doubling of cardiac output.
A tripling of body oxygen consumption was observed. This was due to the increase in cardiac output coupled with an increase in hemoglobin concentration and an increase in body oxygen extraction. This was principally accomplished by an increase in heart rate with a small increase in stroke volume.
The increase in stroke volume was facilitated by an increase in left ventricular contractility as evidenced by an increase in the maximum of the 1st derivative of left ventricular pressure together with an increased rate of relaxation of the left ventricle and an increase in left atrial pressure, which is the filling pressure of the left ventricle. Systemic vasodilation occurred as evidenced by an increase in systemic vascular conductance and a decrease in systemic vascular resistance. This accommodated the increase in cardiac output almost completely so that mean aortic pressure increased only slightly.
Further interpretations of several other parameters are provided in the text protocol. After watching this video, you should have a good understanding of how to chronically instrument animals to make hemodynamic measurements in subsequent cardiovascular experiments.
